CN114230713B

CN114230713B - Method for reducing surface fusion and surface adhesion of high internal phase emulsion in polymerization process

Info

Publication number: CN114230713B
Application number: CN202111677077.9A
Authority: CN
Inventors: 顾子旭; 罗超; 苏卫卫; 杭渊; 刘旭
Original assignee: Suzhou Xingri Chemical Co ltd
Current assignee: Suzhou Xingri Chemical Co ltd
Priority date: 2021-12-31
Filing date: 2021-12-31
Publication date: 2022-12-30
Anticipated expiration: 2041-12-31
Also published as: CN114230713A

Abstract

The present application relates to a method for reducing surface fusion and surface adhesion of a High Internal Phase Emulsion (HIPE) during polymerization in a continuous process for producing HIPE foam comprising the steps of: depositing the HIPE on a conveyor device and simultaneously applying aqueous phases containing a reducing agent before and after the HIPE deposition site; polymerization is then carried out to achieve prevention of HIPE surface fusion and surface adhesion. In the prior art, for the lower surface of the HIPE, because the temperature of the high internal phase emulsion is higher than the temperature of a conveying belt in a deposition area, the temperature of the lower surface of the deposited high internal phase emulsion is rapidly reduced, the polymerization rate of the lower surface of the HIPE is greatly reduced, and the internal phase is fused to different degrees in a polymerization curing furnace.

Description

Method for reducing surface fusion and surface adhesion of high internal phase emulsion in polymerization process

Technical Field

The present application relates to a method for reducing surface fusion and surface adhesion of High Internal Phase Emulsion (HIPE) foams during polymerization when the HIPE is produced in a continuous process.

Background

The high internal phase emulsion refers to an emulsion in which the ratio (W/O ratio) of an aqueous phase as a dispersed phase (internal phase) to an oil phase as an external phase is 3/1 or more, and is hereinafter referred to as HIPE. The use of such HIPE polymerizations to make cellular polymers is well known. The porous polymer produced by HIPE polymerization can give a continuous open-cell foam having a fine pore diameter as compared with the porous polymer produced by using a blowing agent (hereinafter, also simply referred to as HIPE method). After the HIPE is formed, the HIPE may be distributed on a delivery device by a distributor, such as: on a belt and moved to a polymerization reactor to complete the polymerization reaction, thereby obtaining a HIPE foam. One type of polymerization reactor is a curing oven having a single layer or multiple layers, each layer having a belt. The HIPE is continuously moved on a conveyor belt and polymerized, and finally conveyed out of the curing oven.

In a practical continuous production process, it has been found that polymerization by the conveyor belt, with different degrees of inter-phase fusion of the upper (air-side) and lower (belt-contacting) surfaces of the HIPE, produces two results: 1. the pore diameter of the porous polymer is not uniform, so that the absorption performance and the mechanical property are not uniform, and the use characteristics of the porous polymer are influenced; 2. the internal phase fusion results in an increase in the particle size of the internal phase and a decrease in the interfacial area between the aqueous phase and the oil phase, and when the HIPE is polymerized using a water-soluble polymerization initiator, the polymerization rate of the HIPE is significantly reduced due to a significant reduction in the transfer efficiency of free radicals from the aqueous phase to the oil phase, which results in the HIPE not meeting the corresponding mechanical requirements upon leaving the conveyor belt in terms of its random adhesion to the conveyor belt, which adhesion subsequently causes defects in the HIPE, such as: discoloration and reduced structural integrity. Thus, there is a need for a method to prevent intra-surface phase fusion of HIPEs.

Disclosure of Invention

High Internal Phase Emulsions (HIPEs) having varying degrees of internal phase fusion during continuous polymerization, the present invention provides a method for preventing surface fusion and surface adhesion of a HIPE comprising the steps of: depositing the HIPE on a conveyor apparatus and simultaneously applying an aqueous phase containing a reducing agent before and after the HIPE deposition site; polymerization is then carried out to achieve prevention of HIPE surface fusion and surface adhesion. Further, the present invention deposits the HIPE on a conveyor and simultaneously applies aqueous phases containing a reducing agent before and after the HIPE deposition site; then polymerizing to obtain the foam material (porous polymer), and solving the problems of non-uniform pore diameter and unsatisfactory polymerization degree of the porous polymer in the prior art due to the prevention of HIPE surface fusion and surface adhesion.

In the present invention, the HIPE is deposited on the conveying device by a conventional distributor to form a deposition site, so that the HIPE is conveyed with the conveying device into the polymerization reactor, which is a conventional step, and the inventive step of the present invention is mainly characterized in that an aqueous phase containing a reducing agent is applied simultaneously before and after the HIPE deposition site, and an aqueous phase containing a reducing agent is applied before the specific HIPE deposition site, and the aqueous phase is applied on the conveying device; the HIPE deposition site is followed by the application of an aqueous phase containing a reducing agent, which is applied to the HIPE, as is conventionally understood.

In the present invention, the HIPE is formed from a stream of a liquid oil phase containing an emulsifier and a stream of a liquid aqueous phase containing an electrolyte by shear emulsification. The reducing agent is an organic reducing agent, the application is realized by adopting an atomizing spray head, and specifically, an aqueous solution of the organic reducing agent is atomized and sprayed to the front and the back of the HIPE deposition position.

The method for preventing the fusion and the adhesion of the HIPE surface specifically comprises the following steps:

(1) Forming a HIPE, the emulsion formed from a stream of a liquid oil phase containing an emulsifier and a stream of a liquid aqueous phase containing an electrolyte by shear emulsification; depositing the HIPE on a transport device;

(2) Applying an aqueous phase containing a reducing agent to the front end of the HIPE deposition zone; applying an aqueous phase containing a reducing agent to the rear end of the HIPE deposition zone;

(3) Transferring the HIPE on the conveyor belt to a polymerization reactor; the polymerized HIPE was transported out of the polymerization reactor to obtain a foam.

The invention is characterized in that: the aqueous solution containing the reducing agent is applied at a position before and after the position where the high internal phase emulsion is deposited on the conveyor belt (deposition zone) and then is again fed to the polymerization reactor through the conveyor belt. Prior to the present invention, for the lower surface of the HIPE, since the temperature of the high internal phase emulsion is higher than that of the conveyor belt in the deposition area, which leads to a rapid decrease in the temperature of the lower surface of the high internal phase emulsion after deposition, and thus to a large decrease in the polymerization rate of the lower surface of the HIPE, the internal phase is fused to various degrees in the polymerization curing furnace, and the fusion has two results: (1) the pore diameter of the porous polymer is not uniform, so that the absorption performance of a local unit and the mechanical property are changed, and the service performance of the porous polymer is influenced; (2) the internal phase fusion results in an increase in the particle size of the internal phase and a decrease in the interfacial area between the aqueous phase and the oil phase, and when the HIPE is polymerized using a water-soluble polymerization initiator, the polymerization rate of the HIPE is significantly reduced due to a significant decrease in the efficiency of transfer of free radicals from the aqueous phase to the oil phase, which results in the HIPE not meeting the corresponding mechanical requirements upon leaving the conveyor belt in terms of polymerization, which in turn results in adhesion of the surface portion of the HIPE to the conveyor belt, which adhesion subsequently causes defects in the HIPE, such as discoloration and a decrease in structural integrity. And the degree of decrease in HIPE temperature often varies with ambient temperature, creating an uncertain shutdown risk for continuous long-term operation. For the upper surface of the HIPE, oxygen inhibition in air often results in slow polymerization due to the contact of the upper surface with air, which also results in polymerization defects of the upper surface of the HIPE that are consistent with the lower surface. For example: when the belts are arranged in an overlapping, staggered relationship, the HIPE is conveyed sequentially down the belt from belt to belt and finally to the discharge belt. When the HIPE is transferred from one belt to the next, the upper and lower surfaces of the HIPE reverse and the upper layer polymerizes at a low rate, resulting in the lower (second from top to bottom) belt also adhering to the upper HIPE. This adhesion is further exacerbated when the belt transport rate is high and the HIPE monolayer residence time is short.

Drawings

FIG. 1 is a schematic diagram of a HIPE cycle;

FIG. 2 is a process flow diagram of the method of the present invention for preventing HIPE surface fusion and surface adhesion.

Detailed Description

The invention deposits HIPE on conveying equipment, and applies aqueous phase containing reducing agent before and after HIPE deposition position; then polymerizing to obtain the foam material (porous polymer), and solving the problems of nonuniform pore diameter and unsatisfactory polymerization degree of the porous polymer in the prior art due to the prevention of HIPE surface fusion and surface adhesion.

An emulsion (HIPE) is formed from a stream of a liquid oil phase containing an emulsifier and a stream of a liquid aqueous phase containing an electrolyte by shear emulsification. The oil phase consists of an oily monomer and an emulsifier; the water phase is an aqueous solution comprising salts and an initiator. The oily monomer is a polymerizable monomer capable of forming a crosslinked structure by polymerization, and usually contains a polymerizable monomer (I) having 1 polymerizable unsaturated group in the molecule and/or a crosslinkable monomer (II) having at least 2 polymerizable unsaturated groups in the molecule.

As the polymerizable monomer (i):

it is preferred that at least a part of the (meth) acrylate is contained, more preferably 40% by weight or more of the (meth) acrylate, and particularly preferably 60% by weight of the (meth) acrylate. Specifically, the polymerizable monomer (i) includes: styrene, ethylstyrene, α -methylstyrene, vinyltoluene, vinylethylbenzene, methyl (meth) acrylate, ethyl (meth) acrylate, butyl (meth) acrylate, isobutyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, isodecyl (meth) acrylate, lauryl (meth) acrylate, stearyl (meth) acrylate, cyclohexyl (meth) acrylate, benzyl (meth) acrylate. These monomers may be used alone or in combination of two or more.

The amount of the polymerizable monomer (I) is preferably in the range of 40 to 95wt% based on the total weight of the oily monomers. When the amount is within this range, a porous polymer having a fine pore size can be obtained. It is more preferably 50 to 90wt%, particularly preferably 60 to 85wt%. When the amount of the polymerizable monomer (I) used is less than 40% by weight, the resulting porous polymer becomes brittle or unsatisfactory in water absorption capacity. On the other hand, when the amount of the polymerizable monomer (I) exceeds 95% by weight, the strength, elastic recovery force and the like of the resulting porous polymer are insufficient, and sufficient water absorption capacity and water absorption rate cannot be secured.

As the crosslinkable monomer (ii):

there are no particular limitations as long as it has at least 2 polymerizable unsaturated groups in the molecule or can form a crosslinked structure by polymerization, and it can be dispersed or polymerized in a water-in-oil high internal phase emulsion as in the case of the polymerizable monomer (I). Specifically, examples of the crosslinkable monomer (II) include: divinylbenzene, trivinylbenzene, divinyltoluene, divinylxylene, p-ethylvinylbenzene, butadiene, isoprene, pentadiene, ethylene glycol di (meth) acrylate, diethylene glycol di (meth) acrylate, triethylene glycol di (meth) acrylate, polyethylene glycol di (meth) acrylate, 1, 3-butylene glycol di (meth) acrylate, 1, 4-butylene glycol di (meth) acrylate, 1, 6-hexanediol di (meth) acrylate, octyl glycol di (meth) acrylate, decyl glycol di (meth) acrylate, trimethylolpropane tri (meth) acrylate, pentaerythritol di (meth) acrylate, pentaerythritol tri (meth) acrylate, pentaerythritol tetra (meth) acrylate, dipentaerythritol di (meth) acrylate, dipentaerythritol tri (meth) acrylate, dipentaerythritol tetra (meth) acrylate. These monomers may be used alone or in combination of two or more.

The amount of the crosslinkable monomer (II) is preferably in the range of 5 to 60wt%, more preferably 10 to 50wt%, and particularly preferably 15 to 40wt%, based on the total weight of the oil-based monomers. When the amount of the crosslinkable monomer (II) is less than 5% by weight, the resulting porous polymer is insufficient in strength, elastic recovery, etc., or the amount of the porous polymer absorbed per unit volume or weight is unsatisfactory, and sufficient water absorption capacity and water absorption rate cannot be secured. On the other hand, when the amount of the crosslinkable monomer (1-2) exceeds 60% by weight, the porous polymer becomes brittle or the water absorption capacity is unsatisfactory.

The emulsifier is not particularly limited as long as it is a high internal phase emulsion in which the oil phase and the aqueous phase form water-in-oil, and known nonionic emulsifiers, cationic emulsifiers, anionic emulsifiers, amphoteric emulsifiers, and the like can be used. Preferably, nonionic emulsifiers and cationic emulsifiers are used. The combination of both is particularly preferred, and the stability of the HIPE may be improved.

As nonionic emulsifiers:

(1) saturated and/or unsaturated fatty acid sorbitan esters, such as: sorbitan-monolaurate, sorbitan-monomyristate, sorbitan-monopalmitate, sorbitan-monooleate, sorbitan-monostearate, sorbitan-monoisostearate, sorbitan-trioleate, sorbitan-distearate, sorbitan-tristearate;

(2) (Poly) Glycerol- (C) ₁₂ ~ C ₂₂ ) Saturated and/or unsaturated fatty acid esters, such as: glycerol-myristate, glycerol-stearate, glycerol-isostearate, glycerol-oleate; diglycerol-stearate, diglycerol-isostearate, diglycerol-oleate, diglycerol-tristearate; triglycerol-oleate, triglycerol-isostearate; tetraglycerol-monostearate, tetraglycerol-monooleate, tetraglycerol-tristearate, tetraglycerol-pentastearic acid, tetraglycerol-pentaoleate, tetraglycerol-monolaurate, tetraglycerol-monomyristate; hexaglycerol-monostearate, hexaglycerol-monooleate, hexaglycerol-tristearate, hexaglycerol-pentadecanoic acid, hexaglycerol-pentaoleate; decaglycerol-monolaurate, decaglycerol-monostearate, decaglycerol-monomyristate, decaglycerol-monoisostearate, decaglycerol-monooleate, decaglycerol-monolinoleic acid, decaglycerol-distearate, decaglycerol-diisostearate, decaglycerol-tristearate, decaglycerol-trioleate, decaglycerol-pentastearate;

(3) the hydrocarbyl-substituted succinic polyol ester and/or the hydrocarbyl-substituted succinic polyamine ester and/or the hydrocarbyl-substituted succinic hydroxylamine ester.

The nonionic emulsifier has an HLB of 10 or less, particularly 2 to 6. 2 or more of these nonionic emulsifiers may be used in combination, and such combination sometimes improves the stability of the HIPE.

As cationic emulsifiers:

(1) comprising a long chain C ₁₂ -C ₂₂ Dialiphatic, shortChain C ₁ -C ₄ Dialiphatic quaternary ammonium salts, for example: ditalloyl dimethyl ammonium hydrochloride, bihydrogenated tallow dimethyl ammonium hydrochloride, ditridecyl dimethyl ammonium hydrochloride, ditalloyl dimethyl ammonium methyl sulfate, and bihydrogenated tallow dimethyl ammonium methyl sulfate;

(2) comprising a long chain C ₁₂ -C ₂₂ Dialkanoyl (alkenoyl) -2-hydroxyethyl, short-chain C ₁ -C ₄ Dialiphatic quaternary ammonium salts, for example: bistallow acyl-2-hydroxyethyl dimethyl ammonium hydrochloride;

(3) comprising a long chain C ₁₂ -C ₂₂ Dialiphatic imidazolium quaternary ammonium salts, for example: methyl-1-tallowamidoethyl-2-tallowimidazolium methylsulfate, methyl-1-oleylamidoethyl-2-oleylimidazolium methylsulfate;

(4) containing short chains C ₁ -C ₄ Dialiphatic, long-chain C ₁₂ -C ₂₂ Mono-aliphatic benzyl quaternary ammonium salts, for example: dimethyl stearyl benzyl ammonium hydrochloride, dimethyl tallow benzyl ammonium hydrochloride;

(5) comprising a long chain C ₁₂ -C ₂₂ Dialkanoyl (alkenoyl) -2-aminoethyl, short-chain C ₁ -C ₄ Mono-aliphatic, short-chain C ₁ -C ₄ Monohydroxy aliphatic quaternary ammonium salts, for example: ditalloyl-2-aminoethylmethyl 2-hydroxypropyl ammonium methylsulfate, dioleoyl-2-aminoethylmethyl 2-hydroxyethyl ammonium methylsulfate;

2 or more of these cationic emulsifiers can be used in combination to further optimize the thermal stability of the emulsion.

The amount of the emulsifier used is preferably 5 to 15wt%, more preferably 5 to 10wt%, based on the total weight of the oily monomer and the emulsifier. When the amount of the emulsifier used is less than 5wt%, the dispersion stability of HIPE is deteriorated; on the other hand, when the emulsifier is used in an amount exceeding 15% by weight, the resulting porous polymer becomes too brittle and uneconomical.

As the water, besides tap water, pure water and ion-exchanged water, treated HIPE production wastewater can be used. The amount of water used varies depending on the use of the porous polymer. The HIPE foam of the present invention, the use of which is exemplified below:

a) Feminine hygiene articles, for example: pads, pantiliners and tampons;

b) Disposable diapers, incontinence articles, for example: pads, adult diapers;

c) Household care articles, for example: wipes, pads, towels;

d) Cosmetic care articles, for example: pads, wipes;

e) Skin care articles, for example: an absorbent core for pore cleaning;

f) An oil absorbing material;

g) A sound insulating material;

h) A filter material;

the ratio (mass ratio) of the water phase/oil phase (W/O) of the HIPE is not particularly limited depending on the use application, and may be 3/1 or more, but is preferably 8/1 to 140/1. For use in diapers, sanitary materials and the like, W/O is preferably 10/1 to 75/1, more preferably 20/1 to 40/1.

The salt may be selected as long as it is necessary to improve the stability of the HIPE. Preferred electrolytes as the salts are monovalent inorganic salts, divalent inorganic salts, trivalent inorganic salts, such as: water-soluble alkali and alkaline earth metal halides, nitrates, sulfates. Examples include: sodium chloride, calcium chloride, sodium sulfate and magnesium sulfate. Calcium chloride is most preferred in the preparation process of the present invention. The electrolyte is typically used in the aqueous phase of the HIPE at a concentration of about 0.1 to 10 weight percent of the aqueous phase. More preferably, the concentration of the electrolyte is 1-6wt% of the aqueous phase.

Initiator in order to complete the HIPE polymerization in a short time, a polymerization initiator is preferably used. Any one or more of water-soluble, oil-soluble may be used. Such initiator components are typically added to the aqueous phase of the HIPE and may be any conventional water-soluble free radical initiator. Mention may be made, for example, of: azo compounds such as 2, 2' -azobis (2-amidinopropane) dihydrochloride; persulfates such as ammonium persulfate, potassium persulfate, and sodium persulfate; peroxides such as potassium peracetic acid, sodium peracetic acid, potassium percarbonate, sodium percarbonate, etc.

The amount of the polymerization initiator to be used is preferably in the range of 0.5 to 15% by weight, more preferably 1 to 10% by weight, based on 1 part by weight of the total amount of the oily monomers. When the amount of the polymerization initiator used is less than 0.5wt%, the amount of the unreacted polymerizable monomer component increases, and therefore the amount of the monomer remaining in the resulting porous polymer increases. On the other hand, in the case where the amount of the polymerization initiator used exceeds 15% by weight, the control of polymerization becomes difficult, and the mechanical properties in the resulting porous polymer deteriorate, and thus it is also not preferable.

The aqueous phase may further include other various additives, which may be suitably used as long as manufacturing conditions can be improved or HIPE characteristics or properties of the porous polymer can be optimized. For example: to adjust the pH, acids and/or bases and/or buffers may be added; to improve the absorption properties, water-soluble monomers may be added, such as: acrylic acid, vinyl acetate; other functional additives, such as: active carbon, inorganic powder, organic powder, metal powder, deodorant, antibacterial agent, antifungal agent, perfume, various polymers, and emulsifier.

The formation of the HIPE (emulsification process) may be an existing process, and the continuous process for preparing the HIPE of the present invention comprises: one group or a plurality of groups of mixing circulation units consisting of static mixers and pumps are used, and the groups are connected in series; continuously injecting the water phase and the oil phase into the circulating unit at different point positions of the mixed circulating unit; after the water phase and the oil phase are mixed and emulsified through a static mixer, continuously taking out part of emulsion from the downstream of the static mixer by a pump and pumping the part of emulsion back to the upstream of the static mixer; the remaining emulsion downstream of the static mixer is sent to the outlet static mixer and is combined with the aqueous initiator solution, further mixing and shearing are carried out in the outlet static mixer, and the stable high internal phase emulsion is continuously taken out from the outlet static mixer.

The polymerization process of the HIPE is the prior art, the invention applies a reducing agent before and after the HIPE is deposited for the first time, and a specific polymerization device and a conveying device are the prior devices. Polymerization of HIPE is usually carried out by a static heating method which does not deteriorate the stability of HIPE. In this case, batch polymerization may be employed, or continuous polymerization may be employed. Continuous polymerization is preferred in terms of both exerting the polymerization effect and improving the productivity. There can be exemplified a continuous polymerization method in which the HIPE in the form of a sheet or film is continuously cast, heated, polymerized on a belt such as a running belt. The polymerization reactor may be heated by a heat medium such as microwave, near infrared ray, hot steam, hot air, or the like to maintain a temperature required for the polymerization reaction.

In the continuous process of the present invention, the HIPE may be deposited in a belt form on a conveyor belt through a distributor and fed to a polymerization curing furnace to complete the polymerization reaction. The surface of the conveyor belt may be substantially smooth or may include depressions, protrusions, or a combination thereof. The protrusions or depressions may be arranged in any form or order, and may be used to provide a pattern, design, indicia, etc. to the HIPE foam. The belt may comprise one or more materials suitable for the polymerization conditions, examples include materials such as: fluorine resins, for example: polytetrafluoroethylene, tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer, tetrafluoroethylene-hexafluoropropylene copolymer, tetrafluoroethylene-ethylene copolymer; silicone resins, for example: polydimethylsiloxane, dimethylsiloxane-diphenylsiloxane copolymers; heat-resistant resins, for example: polyimide, polyphenylene sulfide, polysulfone, polyethersulfone, polyetherimide, polyetheretherketone, para-aramid resin; thermoplastic polyester resins, for example: polyethylene terephthalate, polybutylene terephthalate, polyethylene naphthalate, polybutylene naphthalate, polycyclohexane terephthalate; thermoplastic polyester-based elastomer resins such as: block copolymers (polyether type) of PBT and polytetramethylene oxide glycol; these materials may be used alone or in combination of two or more.

The invention is characterized in that: the aqueous solution containing the reducing agent is applied at a position before and after the position of the high internal phase emulsion deposited on the conveyor belt (deposition zone), and then sent to the polymerization reactor again through the conveyor belt. Prior to the present invention, the temperature of the high internal phase emulsion on the lower surface of the HIPE, which was higher than the temperature of the belt conveyor in the deposition zone, resulted in a rapid decrease in the temperature of the lower surface of the high internal phase emulsion after deposition, which in turn resulted in a substantial decrease in the polymerization rate of the lower surface of the HIPE, and in the polymerization curing oven, the internal phase fused to varying degrees, which resulted in two results: (1) the pore diameter of the porous polymer is not uniform, so that the absorption performance of local units is changed and the mechanical property is changed, and the service performance of the porous polymer is influenced; (2) the internal phase fusion results in an increase in the particle size of the internal phase and a decrease in the interfacial area between the aqueous phase and the oil phase, and when the HIPE is polymerized using a water-soluble polymerization initiator, the polymerization rate of the HIPE is significantly reduced due to a significant decrease in the efficiency of transfer of free radicals from the aqueous phase to the oil phase, which results in the HIPE not meeting the corresponding mechanical requirements upon leaving the conveyor belt in terms of polymerization, which in turn results in adhesion of the surface portion of the HIPE to the conveyor belt, which adhesion subsequently causes defects in the HIPE, such as discoloration and a decrease in structural integrity. And the degree of decrease in HIPE temperature often varies with ambient temperature, which creates an uncertain shutdown risk for continuous long-cycle operation. For the upper surface of the HIPE, oxygen inhibition in air often results in slow polymerization due to the contact of the upper surface with air, which also results in polymerization defects of the upper surface of the HIPE that are consistent with the lower surface. For example: when the belts are arranged in an overlapping, staggered relationship, the HIPE is conveyed sequentially down the belt from belt to belt and finally to the discharge belt. When the HIPE is transferred from one belt to the next, the upper and lower surfaces of the HIPE reverse direction and the upper layer polymerizes at a low rate, resulting in the lower layer (the second layer from top to bottom) also adhering to the upper HIPE on the belt. This adhesion is further exacerbated when the belt transport rate is high and the HIPE monolayer residence time is short.

According to the invention, the aqueous solution containing the reducing agent is sprayed at the position before and/or after the HIPE is deposited, so that the rapid generation of free radicals on the upper and lower surfaces of the HIPE is greatly promoted, the polymerization reaction rates of the upper and lower surfaces are improved, and the surface fusion and surface adhesion are effectively inhibited. Thus, by spraying the reducing agent, both the amount and quality of HIPE foam produced is increased and the down time required to produce HIPE foam is reduced, such as: the line is shut down to clean the curing oven for single or multiple layers. The reducing agent is a water-soluble reducing agent, and can be exemplified by: sodium bisulfite, potassium bisulfite, sodium thiosulfate, potassium thiosulfate, 2-hydroxy-2-sulfinato acetic acid, L-ascorbic acid and ferrous salt. Sodium hydrogensulfite, 2-hydroxy-2-sulfinato acetic acid and L-ascorbic acid are preferred, and 2-hydroxy-2-sulfinato acetic acid is particularly preferred. The initiator (oxidizing agent)/reducing agent (mass ratio) =1/0.001 to 1/5 is preferable, 1/0.01 to 1/1 is more preferable, and 1/0.02 to 1/0.2 is particularly preferable.

The application of the aqueous reducing agent solution may be selected from the group consisting of: spraying, rolling and knife coating, and preferably adopting a spraying mode. The spray coating may be a combination of one or more atomized sprays, preferably a combination of a plurality of atomized spray heads, the form of the combination being not particularly limited as long as uniform coverage of the aqueous reducing agent solution is ensured. The diameter of the atomized droplets is preferably less than 50 μm, more preferably less than 10 μm, and particularly preferably less than 1 μm. If the droplet diameter is larger than 50 μm, the coverage uniformity cannot be secured.

The HIPE formation temperature (emulsification temperature) of the emulsification step of the present invention is typically in the range of 40 to 95 ℃. When the temperature is less than 40 ℃, the time required for curing may be prolonged, while when the temperature exceeds 95 ℃, the uniformity of the HIPE formed may be deteriorated, and the temperature is preferably 65 to 85 ℃. In order to control the morphology of the HIPE polymer after polymerization, the polymerization temperature is usually from 40 ℃ to 110 ℃, preferably from 60 ℃ to 105 ℃, and more preferably from 85 ℃ to 100 ℃. In the conventional multi-layer curing furnace, the temperature in the furnace is preferably 60 ℃ to 105 ℃, more preferably 85 ℃ to 100 ℃. The heat may come from an intensive oven, infrared heat lamps, microwaves, steam, or other suitable source. As one example of using steam, the heating zone may be a steam tunnel.

"polymerization time" refers to the total time from entering the polymerization zone until exiting the polymerization zone. The method of the present invention is effective as a means for stably producing a porous polymer having uniform properties in a short time within a range of from 10 seconds to 30 minutes by optimizing the initiation of polymerization and the polymerization temperature. The polymerization time is preferably within 30 minutes, more preferably within 10 minutes, particularly preferably within a range of 1 to 10 minutes. The length of the polymerization time can be adjusted by the rate of movement of the transfer device. When the polymerization curing time exceeds 30 minutes, for example, 60 minutes, 120 minutes or the like, the productivity is poor, but the present invention does not exclude such a condition. When the time is less than 1 minute, the strength of the porous polymer may not be satisfactory.

The morphology of the porous polymer obtained in the polymerization step may be any morphology, such as: a sheet. This can be accomplished by distributing the HIPE in sheets in a continuous polymerization process, passing the sheets through a continuous conveying device within the polymerization apparatus, completing the polymerization, and obtaining sheets, which can be further subjected to conventional post-treatments, such as the resulting porous polymer typically being dewatered by compression, aspiration, and combinations of these. Generally, 50 to 98% of the water used can be removed by such dehydration, and the remainder remains attached to and remains in the porous polymer. The dehydration rate varies depending on the application of the porous polymer and the like, and can be appropriately set. The porous polymer obtained in the above step may be dried by heating with hot air, infrared rays, microwaves, or the like, or may be humidified to adjust the moisture content, if necessary. The porous polymer obtained in the above step can be cut into a desired shape and size, if necessary, and processed into products corresponding to various uses.

There are a number of techniques for determining the average cell size of a foam. These techniques include mercury porosimetry, which is well known in the art. However, the most commonly used technique for determining the cell size of foam is simple photogrammetry of foam samples.

For the purposes of the present invention, the average pore size of the foam made by polymerizing such HIPEs can be used to quantify the amount of shear agitation applied to the emulsified material in the static mixer. In particular, after adjusting the oil phase and aqueous phase flow rates to the desired aqueous phase/oil phase ratio, the emulsified material in the static mixer is subjected to shear agitation sufficient to ultimately form a HIPE capable of producing a foam having an average cell size of 5 to 90 μm during subsequent polymerization. More preferably, such agitation should result in an average cell size of the subsequently formed foam of 10-80 μm.

Example 1: preparation of HIPE and preparation of foams with HIPE

To prepare the HIPE, the water, oil and initiator phases included the components shown in Table 1 below.

Table one:

HIPE preparation according to the process flow shown in FIG. 1, the HIPE emulsification equipment was started. The first circulation line is formed by a static mixer a (static mixer Model GX, element combination 35.5 x 24+26.4 x 36, i.e. 24 elements with a diameter of 35.5mm in series with 36 elements with a diameter of 26.4 mm) and a pump a (Herold WK-Pumps, three-blade screw rotor) and its associated lines (lines comprising temperature, pressure and flow measurement points). The aqueous phase was continuously pumped through a tubular heat exchanger at a flow rate of 8100g/min, the temperature of the aqueous phase was controlled at about 80 ℃ and delivered to the inlet upstream of the static mixer a. When the aqueous phase was observed to flow out of the outlet port static mixer (the outlet port was higher than any one unit in the emulsification device so that the pump did not run dry), pump a was started at the theoretical rate of 15000 ml/min. The oil phase was pumped to the inlet of circulation pump A at a flow rate of 320 g/min. At this point the emulsion was formed in static mixer a, a portion of the emulsion downstream of static mixer a entered the inlet of pump a for recirculation, another portion of the emulsion merged with the initiation phase (313 g/min) into the upstream inlet of the outlet static mixer (Model GX,26.4 + 36+20.0 + 36: 36 elements with a diameter of 26.4mm in series with 36 elements with a diameter of 20.0 mm), further mixing and shearing were carried out and a stable high internal phase emulsion was continuously output from the outlet static mixer at a water-to-oil ratio of 26: 1 and a temperature of 75 ℃.

And (4) polymerizing. A group of spraying devices of 2-hydroxy-2-sulfinato acetic acid aqueous solution (concentration: 0.385wt%, flow rate: 31.3 g/min) are respectively arranged at 0.25m in front of and behind the HIPE deposition area, each group of spraying devices is provided with 6 atomizing nozzles, the interval between every two atomizing nozzles is about 10cm, and the particle size of atomized liquid drops is about 300nm. The high internal phase emulsion taken from the HIPE preparation unit was deposited on a conveyor belt (material: PET fiber-reinforced polydimethylsiloxane) and continuously fed into a 5-layer steam polymerization curing furnace (temperature 98 ℃ C.) to complete the polymerization reaction, see FIG. 2. Wherein the distribution width of the HIPE is 70cm, the distribution thickness of the HIPE is 5mm, the conveyer belt runs at the speed of 2.5m/min, the length of each layer of the conveyer belt is 5.5m, and the retention time of the HIPE on each layer of the conveyer belt is about 2min.

Examples 2 to 5 and comparative examples 1 to 5:

the examples and comparative examples were subjected to the variable adjustment as described in Table 2, and the raw materials were the same as in example 1; the effects of examples 1 to 5 and comparative examples 1 to 5 are shown in Table 3.

TABLE 2 adjustment of variables and effects of examples 1 to 5 and comparative examples 1 to 5

TABLE 3 effects of examples 1 to 5 and comparative examples 1 to 5

By comparing examples with comparative examples, it can be seen that the application of the aqueous reducing agent solution can effectively inhibit surface fusion and surface adhesion, and in addition, the tensile strength of the polymer is tested conventionally, and among examples 2 to 4, the tensile strength of the polymer obtained in example 4 is the highest, which is 1.2 times that of example 2 and 1.35 times that of example 3. Thus, by spraying the reducing agent, both the amount and quality of HIPE foam produced is increased and the down time required to produce HIPE foam is reduced, such as: the line is shut down to clean the curing oven for single or multiple layers.

Claims

1. A method for preventing fusion and adhesion of a HIPE surface to a surface, comprising the steps of: depositing the HIPE on a conveyor device and simultaneously applying aqueous phases containing a reducing agent before and after the HIPE deposition site; polymerization is then carried out to achieve prevention of HIPE surface fusion and surface adhesion.

2. The method of claim 1, wherein the HIPE is formed from a stream of a liquid oil phase containing an emulsifier and a stream of a liquid aqueous phase containing an electrolyte by shear emulsification.

3. The method for preventing HIPE surface fusion and surface adhesion according to claim 2, wherein the oil phase stream comprises 85% to 95% oily monomers and 5% to 15% emulsifiers; the aqueous phase stream is an aqueous solution containing 1% to 6% water-soluble electrolyte.

4. The method for preventing surface fusion and adhesion of a HIPE according to claim 1, wherein the reducing agent is a water-soluble reducing agent.

5. The method for preventing HIPE surface fusion and surface adhesion according to claim 4, wherein the reducing agent is one or more of sodium bisulfite, potassium bisulfite, sodium thiosulfate, potassium thiosulfate, 2-hydroxy-2-sulfinatoacetic acid, L-ascorbic acid, and ferrous salt.

6. The method for preventing HIPE surface fusion and surface adhesion according to claim 2, wherein the reducing agent is used in an amount of =1/0.001 to 1/5 based on the mass of the initiator.

7. The method of claim 1, wherein the reducing agent is applied by one of spraying, rolling, and knife coating.

8. The method for preventing surface fusion and surface adhesion of a HIPE according to claim 1, wherein the HIPE formation temperature is in the range of 40 to 95 ℃; the polymerization temperature is 40-110 ℃.